angular contact bearing friction 2

[noreng10]

Using two 20mm (type 7004) bore angular contact bearings with the intention of securing low torque to rotate and accurate spindle rotation under light loads (ounces rather than pounds) Size is determined by bore required for the application. Bearing has small preload from springs. Result generally satisfactory but torgue as, judged subjectively, is subject to developing slight tightness presumably due to balls not tracking uniformally. Housing and spindle are acurately machined but have not been direcly checked.
Has anyone a view on how the tightness might be eliminated?

 

[CESSNA1]

NORENG10: Sounds like you encountering variations in friction in the bearing. That is the torque is low compared to the bearing tolerances and lubricant and friction values. Is oil the lubricant or grease? If grease there is more, and more variable, resistance than oil. The rolling elements are in a cage and should be fairly uniform. That is my 2 cents.

regards
Dave

 

[israelkk]

The same bearing can be made with different precisions for exampele in the American system they are assigned as ABEC 1 to 9. The higher the ABEC No. the more accurate and precise the bearing. For high precision bearings the catalog specifies maximum running and starting torque/friction. I suggest you call the bearing manufacturer (SKF,FAG, Barden,MPB, NHBB, RMB etc.).

 

[noreng10]

israilkk

My problem is that, since retirement , I have no access to manufacturures catloges. Have an out of date SKF which gives plenty of general data but nothing on torque values in relation to such things as bearing grade. Am aware of the American grading and also that the cost increases with precision as one would expect. The project is for an experimental device which would not justify the expense of precision grade. Seems I may have to put up with the torque variation. Intend to try altering the preload which presumably has a bearing on torque. Main idea is for the shaft to have minimal run out and maximun radial rigity (axial load is low) when turned at slow spead (say 10 rpm)

noreng10

 

[Cockroach]

You can typically gain access through the manufacturer website. Simple "google" to a selected manufacturer by searching for "bearing", "bearing tolerances" or something of that nature.

By the way, NTN has a cute little program which does imperial and metric computations for you. I highly recommend it, use it quite often for classification of fits.

Good luck with the search.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[GregLocock]

You could be suffering from lack of preload. The balls may be skidding rather than rolling, occasionally. Of course increasing the preload will increase the average resistance of the bearing, but that may be an acceptable tradeoff.

As ceesna1 says a lighter grade of lube might help.


Alternatively if the seals aren't very good you may be getting dust or grit in them, which will have the same effect.



Cheers

Greg Locock